Adaptive fan reverse core geared turbofan engine with separate cold turbine

ABSTRACT

A turbine engine includes a first fan including a plurality of fan blades rotatable about an axis and a reverse flow core engine section including a core turbine axially forward of a combustor and compressor. The core turbine drives the compressor about the axis and a transmission system. A geared architecture is driven by the transmission system to drive the first fan at a speed less than that of the core turbine. A second fan is disposed axially aft of the first fan and forwarded of the core engine and a second turbine is disposed between the second fan and the core engine for driving the second fan when not coupled to the transmission.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.14/205,847 filed on Mar. 12, 2014, which claims priority to U.S.Provisional Application No. 61/782,610 filed on Mar. 14, 2013.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This subject of this disclosure was made with government support underContract No.: FA8650-09-D-2923/D013 awarded by the United States AirForce. The government therefore may have certain rights in the disclosedsubject matter.

BACKGROUND

A gas turbine engine typically includes a fan section and a core engineincluding compressor section, a combustor section and a turbine section.Air entering the compressor section is compressed and delivered into thecombustion section where it is mixed with fuel and ignited to generate ahigh-energy exhaust gas flow. The energetic gas flow expands through theturbine section to drive the compressor and the fan section and finallyexits through a thrusting nozzle.

Typically, the compressor is axially forward of the compressor andturbine sections. In some gas turbine engine configurations known asreverse flow turbine engines, the turbine section is axially forward ofthe combustor and compressor. Airflow is ducted aft to the compressor,than forward to the combustor and turbine where exhaust gases areexhausted forward and mixed within incoming airflow. Such reverse flowengine can provide performance advantages and efficiencies.

Airflow through the gas turbine engine is typically divided between acore flow path and a bypass flow path. More flow through the bypasspassage as compared to the core flow path typically provides increasedfuel efficiency at the expense of overall thrust. Engines for high speedaircraft include smaller bypass passages to provide greater thrusts.Fuel efficiency is therefore balanced against thrust requirements andsmaller bypass flows are utilized when greater thrusts are desired.

A variable cycle gas turbine engine may switch between highly fuelefficient operation with increased bypass airflow and high speedoperation with less bypass flow with more thrust produced by the coreengine.

Although variable cycle gas turbine engines have improved operationalefficiency, turbine engine manufactures continue to seek furtherimprovements to engine performance including improvements to propulsiveefficiency.

SUMMARY

A turbine engine according to an exemplary embodiment of thisdisclosure, among other possible things includes a first fan including aplurality of fan blades rotatable about an axis. A reverse flow coreengine section includes a core turbine axially forward of a combustorand a compressor. The core turbine drives the compressor about the axis.A transmission system is driven by the core turbine. A gearedarchitecture is driven by the transmission system for driving the firstfan at a speed less than the core turbine. A second fan is disposedaxially aft of the first fan and forwarded of the core engine. A secondturbine is disposed between the second fan and the core engine. Thesecond turbine drives the second fan.

In a further embodiment of the foregoing turbine engine, thetransmission includes a first mode. The second fan is coupled to thetransmission and driven at the speed of the core turbine.

In a further embodiment of any of the foregoing turbine engines, thetransmission includes a second mode. The second fan is driven at a speedless than that of the core turbine and greater than that of the firstfan.

In a further embodiment of any of the foregoing turbine engines, thesecond fan and second turbine are fixed to rotate at a common speed.

In a further embodiment of any of the foregoing turbine engines, thesecond turbine drives the second fan responsive to the transmissiondecoupling from the second fan.

In a further embodiment of any of the foregoing turbine engines,includes a variable vane disposed axially forward of the second turbinefor controlling a speed of the second turbine and thereby the secondfan.

In a further embodiment of any of the foregoing turbine engines, thetransmission includes a first transmission path coupling the coreturbine to the second fan and the geared architecture such that secondfan rotates at a speed common with the core turbine.

In a further embodiment of any of the foregoing turbine engines, thetransmission includes a second transmission path through a gearreduction to drive the second fan at a speed less than that of the coreturbine and greater than the first fan.

A method of operating a turbine engine according to an exemplaryembodiment of this disclosure, among other possible things includesdefining a core gas flow path through a core engine, where the coreengine includes a compressor, a combustor in communication with thecompressor and a core turbine driven by high energy gas flow generatedby the combustor, driving a transmission with the core turbine, drivinga first fan through a geared architecture driven by the transmission,driving a second fan axially aft of the first fan and forward of thecore turbine, the second fan is driven by the transmission at a speedcommon with the core turbine in a first mode, and driving the second fanwith a second turbine disposed axially forward of the core turbine whenthe transmission is in a second mode.

In a further embodiment of the foregoing method, in the second mode thesecond fan is driven at a speed less than that of the core turbine andgreater than that of the first fan.

In a further embodiment of any of the foregoing methods, the second fanand second turbine are fixed to rotate at a common speed and speed ofthe second turbine is varied to change the speed of the second fan whendecoupled from the transmission.

In a further embodiment of any of the foregoing methods, the secondturbine drives the second fan responsive to the transmission decouplingfrom the second fan.

In a further embodiment of any of the foregoing methods, thetransmission includes a first transmission path coupling the coreturbine to the second fan and the geared architecture such that secondfan rotates at a speed common with the core turbine in the first mode.

In a further embodiment of any of the foregoing methods, thetransmission includes a second transmission path through a gearreduction to drive the second fan at a speed less than that of the coreturbine and greater than the first fan in the second mode.

Although the different examples have the specific components shown inthe illustrations, embodiments of this disclosure are not limited tothose particular combinations. It is possible to use some of thecomponents or features from one of the examples in combination withfeatures or components from another one of the examples.

These and other features disclosed herein can be best understood fromthe following specification and drawings, the following of which is abrief description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an example reverse flow turbine engine.

FIG. 2 is a schematic view of the example reverse flow turbine with anexample transmission in a first torque transmitting condition.

FIG. 3 is a schematic representation of the example reverse flow turbinewith the example transmission in a second torque transmitting condition.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates an example gas turbine engine 10 thatincludes a first fan 12 that is driven by a core engine section 14. Thecore engine section 14 in this engine is known as a reverse flow gasturbine engine. The reverse flow gas turbine engine 14 includes acompressor 20, a combustor 18 and a core turbine 16. The core turbine 16is disposed axially forward of the combustor 18 and the compressorsection 20. Incoming air flow 15 proceeds through the first fan 12 intoa core flow path 34 where it is directed to an aft portion of the coreengine 14 into the compressor 20. In the compressor 20, the incoming air15 is compressed and fed to a combustor 18. In the combustor 18, thehigh pressure air is mixed with fuel and ignited to create a high energygas flow. The high energy gas flow expands through the core turbine 16.The high energy exhaust gasses are exhausted through an exhaust mixer 40where the exhaust gasses 42 are mixed with bypass air flows B1 and B2through a corresponding first bypass passage 36 and a second bypasspassage 38. The mixed air flow of exhaust gasses 42 and incoming airflow 15 are then exhausted out of the aft end of the engine 10.

The core turbine 16 drives a shaft 44 that in turn drives a transmission28. The transmission 28 drives the fan 12 through a geared architecture30. The transmission 28 is coupled through a coupling shaft 56 to thegeared architecture 30 such that the first fan 12 will rotate at a speedless than the speed of the core turbine 16 and transmission 28.

The transmission 28 is further coupled to a free spool 26. The freespool 26 includes a second fan 22 that is coupled to a second turbine24. The second turbine 24 is disposed within a core flow path C suchthat incoming air 15 drives the second or cold turbine 24. The secondturbine 24 does not include a rotating shroud for the radially outer tipwithin the core flow passage 34.

The example gas turbine engine 10 includes the reverse flow core engine14 that drives the first fan section 12 and includes the adaptive fan 22that rotates at variable speeds to adapt the engine to various thrustrequirements. As appreciated, a significant amount of incoming air 15 iscompressed and driven through the bypass passages 36 and 38. The moreair flow 15 that is directed and generates thrust through the bypasspassages 36 and 38, the more fuel efficient the engine operates.However, in some instances it is desired to increase thrust, and therebyincrease air flow through the core flow path C is desired. In thesecircumstances, the second fan section 22 is varied in speed todistribute air between the first bypass 36 and the core flow path 34 toprovide the desired specific thrust from the example engine 10.

The second fan 22 is selectively driven by the transmission 28 at aspeed common with the core turbine 16 or decoupled from the core turbine16 to rotate at a speed less than that of the core turbine 16 butgreater than that of the first fan 12.

Referring to FIG. 2 with continued reference to FIG. 1, the exampleengine 10 is shown schematically and includes the transmission 28. Thetransmission 28 includes a clutch 50 and a gear reduction 46. Theexample gear reduction 46 is coupled to the shaft 44 and drives the freespool 26 through a clutch mechanism 48. The clutch mechanism 50 providesfor the direct transmission of torque from the shaft 44 to the freespool 26. The gear reduction 46 drives both the first fan 12 and secondfan 22 at a speed slower than the core turbine 16.

The example engine 10 in FIG. 2 is shown with the transmission 28 in afirst, high speed mode where torque is transmitted along a first loadpath 58 through the clutch 50. The clutch 50 includes no gear reductionor other speed reduction devices and therefore directly transmits thespeed of the core turbine 16 to the free spool 26. The speed of the freespool 26 is therefore equal to that of the core turbine 16.

The first fan 12 is driven by the transmission 28 through the gearedreduction 30 and therefore always rotates at speed less than that of thecore turbine 16. With the first fan 12 and the second fan 22 rotating atmaximum speeds, a maximum amount of airflow is driven through the coreflow path 34 and the first bypass passage 40 to produce a maximum enginethrust.

Referring to FIG. 3, with continued reference to FIG. 1, thetransmission 28 is shown in a second, low speed mode where the examplegear reduction 46 is coupled to the shaft 44 and drives the free spool26 through the clutch mechanism 48. In the second mode of operation,torque is transmitted through the geared reduction 46 and clutch 48 suchthat the second fan 22 will rotate at a speed less than that of the coreturbine 16. The gear reduction 46 further drives the geared architecture30 such that the first fan runs at a slower speed than in with thetransmission in the first mode.

As appreciated, because the core turbine 16 is driving the gearreduction 46 of the transmission 28, both the fan section 12 and thefree spool 26 including the second fan 22 will rotate at a speed lessthan that of the core turbine 16. The second fan 22 or free spool 26will rotate at a speed that is greater than that of the first fan 12 dueto the gear reduction provided by the geared architecture 30. The gearreduction 46 as part of the transmission 28 includes a gear reductionthat provides that the free spool 26 will rotate at a speed greater thanthe first fan 12 but less than that of the core turbine 16.

In the second mode shown in FIG. 3, torque is transmitted through thesecond load path 52 through the gear reduction 46 and the clutch 48. Inthis configuration, the free spool 26 will rotate at a speed that isgreater than that of the first fan 12 but less than that of the coreturbine 16.

Moreover, the clutch 48 may be disengaged and therefore not transmittorque to the free spool 26 such that the second fan 22 is drivenentirely by the second turbine 24. The speed of the second turbine 24 isin turn varied and controlled by way of a variable vane 32. The variablevane 32 is moveable between a first position and a second position by anactuator 54. As appreciated, the first and second positions arepositions that direct air flow into the turbine 24 to govern the speedof the second turbine 24 and thereby of the second fan 22. Thealteration and adjustment of the speed of the second turbine 24 and airswirl of the second fan 22 changes the condition of the core flow C andbypass flow B1. Control of air swirl of the second fan 52 controls flowthrough core flow C and bypass flow B1.

Accordingly, the example gas turbine engine provides for the variationof specific thrust by varying flow through the various bypass passagesand by directing torque in a variable manner between the first fan 12and the second fan 22.

Although a dual annular bypass flow gas turbine engine is indicated, thefeatures of the disclosed invention could be utilized in an engine whereonly a single annular bypass passage is utilized.

Although an example embodiment has been disclosed, a worker of ordinaryskill in this art would recognize that certain modifications would comewithin the scope of this disclosure. For that reason, the followingclaims should be studied to determine the scope and content of thisdisclosure.

1. A turbine engine comprising: a first fan including a plurality of fanblades rotatable about an axis; a reverse flow core engine sectionincluding a core turbine axially forward of a combustor and acompressor, the core turbine driving the compressor about the axis; atransmission system driven by the core turbine; a geared architecturedriven by the transmission system for driving the first fan at a speedless than the core turbine; a second fan disposed axially aft of thefirst fan and forwarded of the core engine; and a second turbinedisposed between the second fan and the core engine, the second turbinedriving the second fan.
 2. The turbine engine as recited in claim 1,wherein the second fan and second turbine are fixed to rotate at acommon speed.
 3. The turbine engine as recited in claim 2, wherein thesecond turbine drives the second fan responsive to the transmissiondecoupling from the second fan.
 4. The turbine engine as recited inclaim 3, including a variable vane disposed axially forward of thesecond turbine for controlling a speed of the second turbine and therebythe second fan.
 5. The turbine engine as recited in claim 1, wherein thetransmission includes a first transmission path coupling the coreturbine to the second fan and the geared architecture such that secondfan rotates at a speed common with the core turbine.
 6. The turbineengine as recited in claim 5, wherein the transmission includes a secondtransmission path through a gear reduction to drive the second fan at aspeed less than that of the core turbine and greater than the first fan.7. A method of operating a turbine engine comprising defining a core gasflow path through a core engine, where the core engine includes acompressor, a combustor in communication with the compressor and a coreturbine driven by high energy gas flow generated by the combustor;driving a transmission with the core turbine; driving a first fanthrough a geared architecture driven by the transmission; driving asecond fan axially aft of the first fan and forward of the core turbine,wherein the second fan is driven by the transmission at a speed commonwith the core turbine in a first mode; and driving the second fan with asecond turbine disposed axially forward of the core turbine when thetransmission is in a second mode.
 8. The method as recited in claim 7,wherein the second fan and second turbine are fixed to rotate at acommon speed and speed of the second turbine is varied to change thespeed of the second fan when decoupled from the transmission.
 9. Themethod as recited in claim 8, wherein the second turbine drives thesecond fan responsive to the transmission decoupling from the secondfan.
 10. The method as recited in claim 8, wherein the transmissionincludes a first transmission path coupling the core turbine to thesecond fan and the geared architecture such that second fan rotates at aspeed common with the core turbine in the first mode.
 11. The method asrecited in claim 10, wherein the transmission includes a secondtransmission path through a gear reduction to drive the second fan at aspeed less than that of the core turbine and greater than the first fanin the second mode.